The present invention relates to a dishwasher, and more particularly to a dishwasher which fits within the counter space typically available for a U.S. residential dishwasher and is operable on a U.S. residential power supply, yet meets the high sanitary requirements of a commercial dishwasher within a convenient cycle time.
Washing involves subjecting the surfaces of the dishes to sprays of a hot water and detergent solution for the purpose of removing food, grease, and other soiling material. Rinsing is the application of hot water to the surfaces of clean dishes.
Etching is a problem with glassware. Etching is the process through which a cloudy film develops on glasses over time. Etching is caused by a combination of several factors, including water softness, detergent, temperature and length of time at which the glassware is exposed to elevated temperatures. Given that detergent and water softness are relatively constant for a residential dishwasher application, it is desirable to avoid holding glassware under high temperatures for extended periods of time. Preferably, dishwashers should not subject glassware to temperatures over roughly 150° F. (66° C.) for longer than roughly 20 minutes or they may induce an unacceptable amount of etching. These standards are not specifically defined, however, since the exact conditions under which etching occurs are not precisely known and vary for different glassware products.
A commercial hot water sanitizing dishwasher must comply with the joint International Standard set by the NSF (National Sanitation Federation) and ANSI (American National Standard Institute)—namely, NSF/ANSI 3-2001. This commercial hot water sanitizing dishwashing machine standard is postulated in terms of three tests: First, the complete cycle shall render dishes free of soil and detergents. Second, the complete cycle shall deliver a minimum of 3,600 HUEs (heat unit equivalents at the surface of the dishes), with varying amounts of HUEs (as set forth in a chart) being added for each second that the surface of the dishes is at a temperature above 143° F. during the rinse cycles. Third, for a hot water sanitizing machine having a stationary rack (as opposed to a conveyer) the machine shall provide either a single temperature of 165° F. (74° C.) for both the minimum wash temperature and the minimum rinse temperature or a dual temperature of 150° F. (66° C.) for the minimum wash temperature and 180° F. (82° C.) for the minimum sanitizing rinse temperature. In both instances, if line pressure is relied upon, the sanitizing rinse pressure should be 20 psi±5 psi (138 kPa±34 kPa).
Accordingly, most commercial hot water sanitizing dishwashers today (e.g., a door-type Jackson TEMPSTAR dishwasher) use a fairly high volume (e.g., about eight gallons) of recirculating water under fairly high pressure (about 20 psi) at at least 150° F. to wash for roughly about 45–48 seconds, then rinse with water at at least 180° F. for roughly about 11–12 seconds (346.8 HUEs/sec.). Such dishwashers have a complete cycle time of about one minute, generate between 3,815–4,161 HUEs, and are said to operate under the dual temperature (150° F./180° F. wash/rinse) implementation of the commercial sanitization standard. However, other commercial hot water sanitizing dishwashers implement the sanitization standard by using 165° F. water for both the wash cycle and the rinse cycle. As all temperatures above 165° F. have a value of 346.8 HUEs, a rinse period of 11 seconds at at least 165° F. generates about 3,814 HUES. Such dishwashers are said to operate under the single temperature (165° F./165° F. wash/rinse) implementation of the sanitization standard. If the temperature of the dishes lags the temperature of the rinse water, additional time (e.g., 20 seconds) may be required to reach the minimum 3,600 HUEs necessary to achieve the sanitization standard.
Commercial dishwashers in the United States (and even residential dishwashers in many European countries) are capable of meeting such stringent requirements in minutes or less since they have available to them an ample electrical supply (e.g., a 220/240 volt, 30–40 amp power supply). On the other hand, a residential dishwasher in the United States typically has available to it only the customary 110–120 volt, 15–20 amp household power supply. Accordingly, the conventional U.S. residential dishwashing systems cannot attain either the 150° F./180° F. or the 165° F./165° F. implementation of the sanitization standard for U.S. commercial dishwashers unless the dishwasher cycle extends for an inordinate amount of time, presumably at least about 90 minutes. The hot water available to a U.S. residential dishwasher is typically at 120° F.–140° F., 120° F. being the most common and 140° F. being the common practical maximum. Accordingly, unless there is a dedicated hot water heater external of the dishwasher to increase the temperature of the hot water supply available to the dishwasher, it is difficult, if not impossible, for the dishwasher—by virtue of its sump reheater alone—to raise the surface temperature of the dishes to above 143° F. and maintain them at that temperature (as necessary to accumulate HUEs) within an acceptable time for a normal residential dishwashing cycle. Thus, for the most part, U.S. residential dishwashers operating under their “normal” wash cycle, even those taking an hour or so for the complete cleaning cycle, typically do not accumulate any HUEs, let alone enough to meet the sanitization standard.
Some residential dishwasher manufacturers offer a “sanitizing rinse” which extends the rinse cycle as required to achieve 3,600 HUEs. Because the residential hot water sanitizing standard (NSF/ANSI 184-2001) eliminates the single and dual temperature requirements, those dishwashers are said to comply with the residential sanitization standard. However, the extension of the rinse cycle to achieve the required 3,600 HUE's causes the total operating cycle time to extend to at least about 70 minutes which is inordinately long.
Informal industry standards and experience for U.S. residential dishwashers dictate, first, that there be at least three, and typically four, cycles—including a bathe or pre-wash cycle, at least one wash cycle, and at least one (preferably two) rinse cycles—to achieve effective cleaning of soiled kitchenware. Each cycle typically requires at least 1.5 gallons of water, typically 1.5–2.0 gallons, in order to obtain the desired cleaning. Second, the dishwasher must be able to operate with the limited U.S. residential power supply (110–120 volt, 15–20 amp power supply) and with the common maximum hot water supply available thereto (140° F.). Third, the dishwasher must operate within a convenient cycle time, and in any case a cycle time which does not involve subjecting glassware to temperatures over roughly 150° F. for longer than about twenty minutes in order to avoid etching of the glassware. Taken in combination, these three informal industry standards—four cycles, limited power, and limited time—pose rather difficult restrictions on the U.S. residential dishwasher, as each of the four cycles involves the introduction of at least 1.5 gallons of water at a maximum of 140° F., which water must be brought up to a higher temperature within a limited period of time using a limited power supply. Complicating the problem of bringing the water to appropriate sanitizing temperatures is the fact that each cycle of the U.S. residential dishwasher—whether bathe, wash, or rinse—begins with the introduction of water which is typically at a maximum of 140° F. The conventional heating element in the recirculating sump of the U.S. residential dishwasher has available to it only about 800 Watts of power (that is, the standard U.S. residential electrical power input minus the amount of power required to run the sump recirculating pump and controls).
The conventional heating element of a dishwasher (located in the recirculating sump) must raise the temperature of not only the 1.5–2.0 gallons of water present in a given cycle (equivalent to 12–16 lbs. of water), but also the kitchenware to be cleaned, including dishes, pots, pans, silverware and like kitchen utensils (typically about 20–30 lbs.), and the cavity/rack/spray-on system of the dishwashing cavity (typically about another 46–63 lbs.). In summary, the sump heating element can typically provide an increase in temperature of the system (that is, the approximately 78–109 lbs. of water, kitchenware to be washed, and dishwasher cavity surfaces) of about 1° F. per minute. The power supply must not only feed such heating element, but also perform the non-heating functions of the dishwasher—e.g., driving the pump that circulates the water under pressure into and around the cavity, driving the controls of the consumer interface, and the like. Thus it is not surprising that the time required to meet either implementation of the commercial sanitization standard would be longer than an hour for a U.S. residential dishwasher.
The time required for a sanitizing cycle is determined by various variables. A prime variable is the hot tap water temperature—that is, the temperature of the water entering the dishwasher from the hot water tap. The U.S. Department of Energy urges that the water heater of a residence be set at no more than 120° F. However this variable is dependent upon household use of the hot water shortly prior to initiation of the preheat cycle (e.g., for pre-dinner bathing of children) as these demands upon the system may result in only a limited quantity of available hot tap water at 120° F. Another significant variable relates to the nature of the tub construction, the conventional stainless steel tub wash system weighing about 63 lbs of high heat capacity metal and the newer plastic tub wash system weighing about 46 lbs of a plastic having a lower heat capacity than metal and thus providing superior insulation. A final significant variable is the dishwasher load which is set by the AHAM standard at about 32 lbs, but may typically be as low as 16 lbs when the racks are not filled completely with kitchenware or where lightweight plastic kitchenware replaces heavier earthenware kitchenware.
Separate and apart from the constraint imposed on a U.S. residential dishwasher by the limited power supply available, there is also a constraint on the size or volume of a U.S. residential dishwasher. Both builder-supplied dishwashers (for new home construction) and replacement dishwashers are expected to fit within a given volume of “cabinet space,” which has become standardized over time at about 35″×24″×23″ to provide a dishwasher enclosure of about 11 cubic feet. The standard volume evolved in a way that allowed the dishwasher to fit under a counter at the standard kitchen counter height, with a door at a height at which consumers felt comfortable loading dishes, and a combined height and width that didn't take up too much cabinet space yet held a reasonable number of dishes. Taking into account the height of the lower tray rollers, the thickness of the door itself, and the space between the bottom of the lower tray and the bottom of the dishwasher cavity leaves approximately 6.8–7.4 inches between the floor and the bottom of the dishwashing cavity (about 4.8–6.0 inches for a “tall tub” dishwasher). Within this limited height must fit most of the working parts of the dishwasher (e.g., inlet water connection, electrical power connection, inlet water valve, motor, valves, hoses, controls, etc.) external of the dishwashing cavity. Any advancement in dishwashers which does not fit within the existing industry standard for cabinet space will simply not be commercially viable. Fortunately, due to technological advances in plastics forming, motor controls and the like, the size of the working parts of dishwashers has shrunk over time since their introduction, and, as a result, some of the space under the dishwashing cavity and above the floor is now available for improvements in the residential dishwasher.
Accordingly, it is an object of the present invention to provide a sanitizing dishwasher which in one preferred embodiment operates on a conventional U.S. residential power supply.
A further object is to provide such a dishwasher which in one preferred embodiment occupies only the conventional U.S. residential dishwasher cabinet space.
Another object is to provide such a dishwasher which in one preferred embodiment surpasses the joint NSF/ANSI standard for commercial hot water sanitizing dishwashers.
It is also an object of the present invention to provide a dishwasher which in one preferred embodiment has a cleaning cycle which is effective for commercial sanitization purposes, yet shorter in length than the non-sanitizing cleaning cycle of the conventional U.S. residential dishwasher.
It is another object to provide such a dishwasher which in a preferred embodiment fits within the conventional U.S. residential dishwasher cabinet space and uses the conventional U.S. residential power supply, but achieves within a convenient cycle time the same standard of sanitization as is set for commercial hot water sanitizing dishwashers.
It is yet another object to provide such a dishwasher which in a preferred embodiment achieves a residential hot water sanitizing standard in less than 15 minutes.
It is a further object to provide such a dishwasher which is simple and inexpensive to manufacture, use and maintain.